Problem started on March 29, 2009 (worked just fine before that date, for about 3 month)
Same problem here,
Verizon FIOS 20/20, 2 t-mobile@home routers(latest firmware 1.0.15, tried 1.0.9 and 1.0.4 but the same issue) 3 numbers, all numbers are affected, tried different answering systems and PBXs, all the same. incoming tones are not being recognized. Called t-mobile ;)). Waste of time as usually.
Outgoing DTMF is just fine, incoming are too short and barely audible